Extremely sensitive, low-cost acoustic sensors are required for a wide range of applications, many of which involve operation under hostile environmental conditions. Typical examples are under water acoustic sensors for detection of deep diving submarines and geophones used to record the response of the earth to acoustic impulses applied thereto in the search for minerals and petroleum. It has been recognized that fiber optics may allow the construction of rugged, high performance microphones and, in particular, the United States Navy has successfully developed an approach based on the comparison of light passed through a reference optical fiber shielded from acoustic noise with light passed through a second signal fiber. This approach is reported in the paper entitled, "Fiber-Optic Hydrophone" by J. A. Bucaro, et al.
Unfortunately, the available devices are orders of magnitude less sensitive than what is desired for some applications. Also, many sensitive acoustic devices have the need, heretofore, unfulfilled, for automatic noise suppression, low cost, and ease of incorporation in acoustic sensor arrays.